Quenching is a kind of heat treatment process, in which the workpiece is heated to a temperature and preserved for a period of time, and then put into the coolant quickly. Quenching process can improve the hardness and wear resistance of the workpiece. Therefore, the quenching process has been applied to various kinds of tool, die, measuring device and the parts which required high surface wear resistance such as gear, roller and so on. Moreover, some steel with special property can get particular physical and chemical properties by quenching processes, e.g. the ferromagnetic property of permanent magnetic steel can be strengthened, and the corrosion resistance of the stainless steel can be enhanced.
Quenching process is mainly used for the steel parts. The mechanism of quenching process for the steel parts is that: when the material was heated up to a critical temperature, all or most of the microstructure will be transformed to the austenite. Then, the steel parts are put into the coolant to be cooled quickly, and the austenite will be transformed to martensite or bainite. Generally, the parts have to be tempered after the quenching process to improve the tensile strength, hardness, wear resistance, fatigue strength and toughness, and then to meet the various requirement of the parts and tool. Quenching process has been widely used in the modern mechanical manufacturing area. Almost all of the important parts used in the machine, especially in the automotive, airplane and rocket area, should be quenched.
Applying the additional energy field into the quenching process can improve the quenching effect. So far, the research is just concentrated on the electromagnetic field. For the carbon steel and low alloy steel material, martensite is ferromagnetic phase, and the austenite is paramagnetic phase. Under the action of the magnetic field, the free energy of the martensite will be decreased due to the magnetization. Therefore, the magnetic field can improve the transformation of the austenite to the martensite. Moreover, the lamellar martensite has the magnetostriction under the action of magnetic field because the misorientation of the lamellar martensite is different, which cause the lattice of the martensite phase and austenite phase to be distorted. This elastic distortion energy can also improve transformation of the austenite to the martensite and increase the nucleation rate of the martensite. Therefore, the electromagnetic energy can refine the martensite and decrease the content of retained austenite.